Diesel powered systems such as, but not limited to, off-highway vehicles, marine diesel powered propulsion plants, stationary diesel powered system and rail vehicle systems, or trains, usually are powered by a diesel power unit. With respect to rail vehicle systems, the diesel power unit is part of at least one locomotive and the train further includes a plurality of rail cars, such as freight cars. Locomotives are complex systems with numerous subsystems, with each subsystem being interdependent on other subsystems.
A diesel-electric locomotive typically includes a diesel engine coupled to drive electrical power sources including a main alternator and an auxiliary alternator, each alternator producing alternating current (AC) electrical power. Such alternators are typically salient pole, synchronous dynamoelectric machines. The main alternator may be coupled to power one or more traction motors, and the auxiliary alternator may be coupled to power locomotive auxiliary electrical equipment. A frequency of an AC output of the alternators is proportional to engine speed in revolutions per minute (RPM). For example, at a typical locomotive engine speed of 1050 RPM, an AC output of 105 Hertz is produced for a 12 pole alternator. Some auxiliary equipment, such as fans or blowers used for cooling, may need to be operated at frequencies different than a frequency provided by the auxiliary alternator at normal engine speeds to achieve a desired cooling effect and/or to achieve a better fuel efficiency. In the past, cycle skippers have been used to provide discrete levels of power at certain fixed frequency multiples based on power phases of the supplied AC power. Such solutions typically require additional equipment in the form of cycle skippers that add to the expense and maintenance of the locomotive auxiliary power systems. Alternatively, a frequency of AC power produced by the auxiliary alternator may be varied by adjusting an engine speed to achieve a desired power frequency. However, varying the engine speed may not be practical in some applications and may result in increased fuel usage and emission production during periods of increased cooling demand.
Owners and/or operators of locomotives, off-highway vehicles, marine diesel powered propulsion plants, and/or stationary diesel powered systems desire to optimize fuel efficiency and emission output so as to save on overall fuel consumption while minimizing emission output.